Does anybody know where I can buy a battery for a Nikon P7100 without paying over list. Why are they in such demand? Is it because it also fits the new D3200? Every dealer that does have them in stock seems to be over profiting on the sale of this battery–some at bandit prices.

The dealers charge high prices because they don't get them cheap from Nikon. Only unscrupulous dealers charge more than you can buy from the Nikon Store. One additional reason is that the EN-EL14 is also used by the P7000, and any owners of that camera that upgraded their firmware to ver. 1.2 (the version that fixed most of the focusing errors) found that their inexpensive EL-EL14 third party batteries no longer worked and they had to replace them with Nikon's EN-EL14. Here's one for $13 that worked with the previous firmware :